Two igniter plugs may be provided in a combustion chamber in order to alternate between one-point ignition and two-point ignition. Th1s technology is applied to, for example, a direct-injection engine in which the combustion chamber is provided with a fuel injection valve, whereby under low-load conditions, stratification combustion is effected by energizing an igniter plug provided to the combustion chamber in order to improve energy efficiency, and under high-load conditions, this is switched to homogeneous combustion in order to obtain high output. At the same time, EGR (Exhaust Gas Recirculation) is effected in order to reduce the NOx generated largely under high-load conditions. EGR reduces the rapidity of combustion, thereby reducing combustion efficiency. Reduction of the rapidity of combustion in the EGR environment is offset by energizing another igniter plug in addition to the first-mentioned igniter plug.
In the case of ignition at two or more points as described above, a first igniter plug can be provided at the center of the combustion chamber and a second igniter plug can be provided at a location other than the center of the combustion chamber. When ignition is effected by using these two or more igniter plugs, the rapidity of combustion can be increased and energy efficiency can be improved.